In recent years, minimally invasive surgery has been gaining increased popularity. This type of surgery, utilizing an endoscope through minor skin incisions, has multiple applications in gynecology, general surgery, thoracic surgery, urology and orthopedics.
The trocar/cannula provides the portal for inducing instruments into the body cavities of interest. In the case of laparoscopy, the trocar/cannula provides the portal into the peritoneal cavity.
Traditionally, trocar and cannula are reusable and are made of metal. The cannula consists of a sleeve, the channel through which the instruments can pass. In order to insufflate the abdominal cavity with carbon dioxide, a side port usually is placed near the top of the cannula for the intake of gas. For the abdominal cavity to remain inflated while an instrument is not in the cannula, a valve in a non-invasive portion of the cannula prevents gas from escaping through the cannula. The valve usually uses a trumpet or trapdoor mechanism.
Typically, trocar and cannula are reusable. However, after use, blood and other body fluids contaminate the cannula parts. With the increasing awareness of risks of transmission of diseases, such as HIV virus and hepatitis, through blood and other body fluids, cleaning and sterilizing the trocar and cannula are of great concern.
Common cannula present the difficulty in cleaning and sterilizing after each use. In particular, side port and valve mechanisms, which usually include springs and mechanical parts, are hard to disassemble and clean.
Though the most difficult part of a cannula to clean and sterilize is the non-invasive portion containing the small side port for gas and the gas retention valve with all its mechanical parts, the cannula sleeve itself is usually only a hollow tube that can be easily cleaned and sterilized.
To address this problem of cleaning and sterilization, a disposable cannula/trocar was introduced a few years ago. These disposable instruments are usually made of plastic and are single-use devices. While reducing the problem of contamination and cleaning costs, these devices introduce two additional problems. First, because the plastic cannula sleeve is electrically nonconductive, its electrical properties can cause electrosurgical damage as described below. Moreover, the disposable plastic cannula/trocar impose a high-cost per use.
The problem of electrosurgical damage is known in the art. Essentially, where a monopolar electrode is used, especially through a metal laparoscope in the cannula, capacitive coupling potentially can lead to arcing between the laparoscope and any nearby organs. This occurs primarily in nonconductive sleeves because they are unable to dissipate the electrical energy through the abdominal or similar wall as a metal cannula sleeve can. Even where an electrode is not inserted through the cannula, charge coupling within the body may occur due to the touching of an active electrode to a laparoscope with a plastic cannula. This can result in electrical discharge to nearby organs. In abdominal surgery, this occurs most frequently in the bowel.
The lower risk associated with reduced contamination risk is thus offset by a higher risk of electrosurgical damage. One attempt to reduce the problem of contamination while retaining conductivity employs a two-part metal cannula. While improving the cleaning process, the non-invasive portion is reused raising the risk of contamination. Further, the non-invasive portion does not lend itself to easy manufacture. Moreover, there is no provision for using varying caliber invasive portions with a single non-invasive portion or structure.